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  1. #1
    Join Date
    Mar 2012
    Location
    Las Vegas, NV
    Posts
    17

    Bubbles in a Sight Glass

    You guys will have to excuse me, as I have less than 3 years and only one year in commercial. I also have little experience in refrigeration but occasionally have to do it.
    I have seen on several occasions a sight glass on a rack that I am charging having bubbles in it, though dry, but the subcool is correct. I would wait aroung for twenty minutes to a half hour thinking they would go away. They didn't. I would add a little 22 and the bubbles would persist, though my subcooling would go up 1 degree. I would verify my split in the walk-in and all was good, so I left it and no problems or call backs.
    I would never have thought about it again, but I have found this website and have been studying these forums and it raised the question. I do not have specific data on a specific job, as this happened to me twice last year at different locations and only now am I curious about it.
    Both days would have been around 110 degrees in the desert, maybe 125 on the roof, with low relative humidity, and I was working on walk-in refrigerators. I am just asking if this is common or if there was an underlying problem that I was unaware of. If I didn't provide enough info for the real pros I appologize.

  2. #2
    Join Date
    Mar 2012
    Location
    Las Vegas, NV
    Posts
    17
    As an add on to my original thread, the fridge in my head was on a rack with two other compressors with sight glasses. Neither of them had bubbles in the sight glass, but they were both to the walk-in freezer and they used a different refrigerant, 404A. I did not use them for a reference for this reason.

  3. #3
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,579
    Quote Originally Posted by golden1019 View Post
    You guys will have to excuse me, as I have less than 3 years and only one year in commercial. I also have little experience in refrigeration but occasionally have to do it.
    I have seen on several occasions a sight glass on a rack that I am charging having bubbles in it, though dry, but the subcool is correct. I would wait aroung for twenty minutes to a half hour thinking they would go away. They didn't. I would add a little 22 and the bubbles would persist, though my subcooling would go up 1 degree. I would verify my split in the walk-in and all was good, so I left it and no problems or call backs.
    I would never have thought about it again, but I have found this website and have been studying these forums and it raised the question. I do not have specific data on a specific job, as this happened to me twice last year at different locations and only now am I curious about it.
    Both days would have been around 110 degrees in the desert, maybe 125 on the roof, with low relative humidity, and I was working on walk-in refrigerators. I am just asking if this is common or if there was an underlying problem that I was unaware of. If I didn't provide enough info for the real pros I appologize.
    A rack system would typically be charged to a certain receiver level than to subcooling. If you don't have a good receiver level, you are not properly charged.

    Certain racks are charged to subcooling, but I don't expect you'd see them in that climate.

  4. #4
    Join Date
    Mar 2012
    Location
    Las Vegas, NV
    Posts
    17
    I also thought that the idea behind a rack was to use the same condenser. This one had two. Obviously for different refrigerants. Is this common, uncommon, or a retrofit?

  5. #5
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,579
    Quote Originally Posted by golden1019 View Post
    I also thought that the idea behind a rack was to use the same condenser. This one had two. Obviously for different refrigerants. Is this common, uncommon, or a retrofit?
    was it a split condenser arrangement?

    Not uncommon as a control. Maybe a little uncommon to see two separate coils used as a split.

    You aren't going to get away with 2 refrigerants in the same system, though.

  6. #6
    Join Date
    Mar 2012
    Location
    Las Vegas, NV
    Posts
    17
    Yes, obviously it had two condensers, one for the the 22 in the fridge and and another for the 404 in the freezer. My mistake with wording. Also, thank-you for responding to my thread. I also don't remember seeing a receiver in the rack. I am not a refrigeration guy, though I am learning. Would it have been in the evap unit in the box? I also am not sure what you were talking about with the receiver level as opposed to subcooling, as it had a TXV. I remember seeing the bulp on the suction line. Is this a different method of charging than S/H or S/C?
    Once again, please excuse me for being inexperienced in refrigeration.

  7. #7
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,579
    Quote Originally Posted by golden1019
    Yes, obviously it had two condensers, one for the the 22 in the fridge and and another for the 404 in the freezer. My mistake with wording. Also, thank-you for responding to my thread. I also don't remember seeing a receiver in the rack. I am not a refrigeration guy, though I am learning. Would it have been in the evap unit in the box? I also am not sure what you were talking about with the receiver level as opposed to subcooling, as it had a TXV. I remember seeing the bulp on the suction line. Is this a different method of charging than S/H or S/C?
    Once again, please excuse me for being inexperienced in refrigeration.
    Oh wow!

    You have 2 racks, then.

    The receiver will typically be a large tank near the compressors. On newer equipment, you may find it under the condenser.

  8. #8
    Join Date
    Oct 2008
    Location
    Central Oregon
    Posts
    14
    What exactly was your subcooling? Maybe your still low. BTW where in the world are you where it is 125 on the roof? I want to go there now .I'm freezing.

  9. #9
    Join Date
    Mar 2012
    Location
    Las Vegas, NV
    Posts
    17
    My subcooling was 20 degrees. I was told this by a tech that was familiar with the system, but was not on sight. I asked him what the subcool should be over the phone and he said 20. Most charts you see in Las Vegas don't go into our temperature ranges, this means you have to adapt because your equipment does work in an extreme, but there are no no guidelines at this outside ambient. I am in Las Vegas, and right now it is about 83/65. Perfect. Thank-you for your attention to my thread.










    las Vegaas

  10. #10
    Join Date
    Feb 2004
    Location
    British Columbia, Canada
    Posts
    521
    It sounds like the systems that you are working on are not actual racks but separate condensing units mounted on a common shelf or stand? If so, these would probably be "satellite" units.
    A genuine rack system can have multiple systems, each with its own refrig type specific to the application it is used for. It will generally serve more than one fixture per system. They are usually split up between low and medium temp systems but with 404A you can use this one type of gas for most systems if properly designed of course. The different fixtures (walkins, coffin cases, deli islands, multidecks, etc) are controlled with EPR valves, solenoid valves, etc to achieve proper cooling in each.

    I'm thinking that if your pressures, superheat and subcooling are all good,
    with 22 you will want to add refrigerant until the bubbles disappear. You always want a solid column of liquid refrigerant at the thermostatic expansion valve. When you don't you may experience excessive subcooling of the refrigerant which causes sub freezing temps at the coil on medium temp systems. That is why you will see ice build up on the bottom few inches on the evap coil when there is a shortage of refrigerant.

    Check first for fixture temperature, a warm case or warm/hot product in the case can cause bubbling at the sight glass.

    However, with some of the new gases, small bubbles at the sight glass can be acceptable and you may actually overcharge the system trying to get rid of them.

    Critical charge systems are a whole different story...

    Does the system you are working on serve only one fixture or multiple fixtures?

    There are many facts that could explain your situation, my post does not cover them all by any means.

    Post some pics if you can, that would help.

  11. #11
    Join Date
    Jan 2012
    Location
    Central New Jersey USA
    Posts
    65
    Also keep an eye on the superheat. If the Expansion valve is "hunting" (opening and closing rapidly) you may see bubbles appear and disappear. The TXV bulb needs to be mounted tightly. You also need to have accurate measuring instruments, calibrate the guages and check you temperature meter with ice and water= 32* F. Do not use a temperatuer gun as it is affected by color, light and stuff that shines. A thermocouple type temperature probe works well if it is covered with some insulation.

    Good luck

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